Chapter 3 The Local Anesthetic and Pain Relief Activity of Alkaloids Havva Sayhan, Serbülent Gökhan Beyaz and Ahmet Çeliktaş Additional information is available at the end of the chapter http://dx.doi.org/10.5772/intechopen.69847 Abstract Alkaloids have been known for several centuries and have been mainly obtained from natural sources that presented important properties with biochemical, pharmacologi- cal, and medical effects in living organisms. Alkaloids are derived from amino acids like other important molecules in the functioning of life in our body. Hence, alkaloids are considered as pharmacologically important. Alkaloids are secondary metabolites widely distributed in leaves, stem, root, and fruits of plants which synthesize them. However, administration and consumption of them at right doses are beneficial in terms of health; excess doses will be definitely poisonous and may cause even death. The pharmacological activities of alkaloids are quite diverse. They are important natural products with a wide range of medicinal properties including relief of pain (e.g., morphine), analgesic (e.g., codeine), antiarrhythmic (e.g., quinidine), antibacterial (e.g., chelerythrine), antiasthma (e.g., ephedrine), cholinomimetic (e.g., galantamine), and vasodilatory (e.g., vincamine). Keywords: alkaloids, local anesthetics, pain relief, analgesia, natural products, mechanism of action, bioorganic chemistry 1. Introduction MERGEFORMAT plants have been used from ancient times as an excellent source of phar- maceutical compounds in the treatment of diseases and have solid impact on human health. Modern chemistry and material sciences have identified the compounds with pharmacologi- cal properties for the development of new drugs. Hence, they have played a major role in drug discovery as natural products and synthetic materials which do not exist in the nature and can only be produced. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 58 Alkaloids – Alternatives in Synthesis, Modification and Application The presence of some chemical substances in plant tissues produces a physiological action on the body and regulates the metabolic activity. For example, these chemicals give plants their color or act as defense system based on their toxic effects. Alkaloids have been known for several centuries and have been mainly obtained from natural sources that presented impor- tant properties with biochemical, pharmacological, and medical effects in living organisms. Alkaloids are secondary metabolites widely distributed in leaves, stem, root, and fruits of plants which synthesize them. However, administration and consumption of them at right doses are beneficial in terms of health; excess doses will be definitely poisonous and may cause even death. Many alkaloids extracted from plants showed anticholinesterase activity [1, 2] and antioxidant [3], anxiolytic [4], antimicrobial [5], anti-HIV [6], antiparasitic [7], anti- inflammatory 8[ ], and antidepressant [9] properties. After the recognition of vital importance of these nitrogenous secondary metabolites, they are found in animals too [10]. In spite of the investigations on the biological activity of some alkaloids, only a few could be produced com- mercially due to their complex chemical structures. The synthetic production of some impor- tant alkaloid is more common than their isolation from plants. In addition, there are other synthetic compounds that are closely related to the natural alkaloids but lack of some typical properties (e.g., homatropine) [11]. Alkaloids display antimicrobial and antiparasitic properties, act as narcotics, can alter DNA, have an important role in the immune systems, and treat cardiovascular and metabolic dis- orders, inflammation, infectious diseases, and miscellaneous problems [10, 12–19]. Therefore, modern medicine tends to produce pharmaceuticals on the basis of natural alkaloids and alkaloids with modified structure such as aconitine, ajmaline, berberine, morphine, caffeine, theophylline, ephedrine, atropine, scopolamine, reserpine, and pilocarpine. There are several morphine-containing drugs that are used in cases of surgical operations and postoperative treatments (i.e., Morphalgin, Spasmofen, and Morphin) [20, 21]. 2. History The human race has used alkaloids in the scope of medicinal and pharmaceutical importance even before their discovery as chemical molecules. There are records from the Babylonian, ancient Hebrew, Egyptian, Chinese, Greek, and Assyrian times, such as Sanskrit writings and the works of Hippocrates, showing that they were all familiar with medicinal plants and alka- loids to improve the health in the early 5000 BC. The most prominent examples of medicinal plants based on the earlier beliefs and knowledge were myrrh, opium, cannabis, aloes, cas- sia, and hemlock. For example, native people of America and tribes in the Amazon used the alkaloid quinine in herbal before its official use in the cure of uncomplicated malaria in 1638. The latex of opium poppy (Papaver) was already in use in the Middle East and Greece at 1200 BC. The roots of the mandrake plant were used because of sedative properties from the time of Hippocrates (ca. 400 BC). All alkaloids cause a physiological effect on the human body, and different poisonous alkaloids such as the ergot alkaloid, aconitine, and tubocurarine have been used for toxic purposes in ancient time. The poisonous alkaloids were prepared from plants (also from animal sources) and used as poisons for arrows by hunters in different parts The Local Anesthetic and Pain Relief Activity of Alkaloids 59 http://dx.doi.org/10.5772/intechopen.69847 of the world. Literature also refers that some alkaloids including aconitine, atropine, colchi- cine, coniine, ephedrine, ergotamine, mescaline, morphine, strychnine, psilocin, and psilocy- bin have been used in executions. Philosopher Socrates was sentenced to death by consuming a cup of hemlock which contains the alkaloid coniine in 399 BC [11, 22–31]. Despite the fact that alkaloids have been in use for ages, actual studies on isolation from plants as relatively pure compounds occurred only in the beginning of the 1800s. In the late 1700s, Lavoisier and others introduced the new developments in chemistry that leads many chemists to try to isolate the active ingredients in plants. The German pharmacist’s apprentice Friedrich Sertürner discovered the morphine in opium poppy by dissolving it in acid and neutralizing it with ammonia in 1804 for the first time in history. Morphine is considered for clinical purposes primarily a safe and effective way of pain relief. Although morphine is used clinically, drug addiction began with morphine and related substances. When Sertürner proved that the substance (morphine) he had isolated was indeed responsible for the actions of opium, chemists had isolated several other medically important substances such as qui- nine, strychnine, and caffeine around that time. While the first use of the name “alkaloids” was in 1819 by a German chemist Carl F.W. Meissner, the term had an extensive usage after the publication of an article in the chemical dictionary of Albert Ladenburg in the 1880s [11, 22–24, 32–37]. 3. Properties An exact and precise definition is somewhat difficult because of differences between the research fields of biology, medicine, and chemistry. The term alkaloid (alkali + oid) means alkali-like substance, and names of alkaloids end in -ine (e.g., atropine, cocaine, and mor- phine). Many methods have been proposed for the classification of alkaloids such as phar- macological, taxonomic, chemical, and biosynthetic classification. Although chemical classification based on the carbon skeleton is the most accepted way of classification, here we will use the pharmacological one depending on the physiological response. Alkaloids are a class of organic compounds that is made up of carbon, hydrogen, oxygen, and nitrogen. In addition, sulfur and rarely other elements such as chlorine, bromine, and phosphorus are also included in the alkaloids. Primary nitrogenous metabolites including amino acids and polymer of amino acids serve as precursors for alkaloids and are usually largely retained in the structure where the nitrogen in the alkaloid molecule is derived. In particular, alkaloids are synthesized from amino acids mostly derived from four different amino acids: lysine, phenylalanine, tyrosine, and tryptophan. To this respect alkaloids show similar structural features to the originated amino acid (shown in Figure 1). Alkaloids usually have one or more heterocyclic ring structure which includes at least one nitrogen atom in the ring. Nevertheless, the nitrogen atom is not within a carbon ring in some alkaloids such as mescaline. They are alkaline in nature due to the nitrogen content that they can absorb acid or hydrogen ions making them a base; however, some do not exhibit alkaline properties. The fact remains that the precise position of the nitrogen atom in the carbon ring or molecule varies with different alkaloids that determines the properties of them [24, 38–40]. 60 Alkaloids – Alternatives in Synthesis, Modification and Application Figure 1. The amino acids used for alkaloid biosynthesis. From the first impression, the term “secondary metabolite” looks like it is used to describe